Random Noise Component Research Articles

Predictive self-organizing map for vector quantization of migratory signals and its application to mobile communications

This paper proposes a predictive self-organizing map (P-SOM) that performs an adaptive vector quantization of migratory time-sequential signals whose stochastic properties such as average values of signals in each cluster are varying continuously. The P-SOM possesses not only the weight corresponding to the signal values themselves but also those related to the time-derivative information. All the weights self-organize to predict appropriate future reference vectors. The prediction using the time-derivative weights enables the separation of continuously varying components form random noise components, resulting in a better performance of the adaptive vector quantization. That is to say, the stationary random noise components are captured by the ordinary weights, whereas the migrating components are captured by the first (and higher) order time-derivative ones. An application to a mobile communication receiver using quasi-coherent detection is presented. By utilizing both the ordinary and time-derivative weights consistently, the P-SOM generates a predictive reference vectors and quantizes the migratory signals adaptively. Simulation experiments on the bit-error rates (BERs) demonstrate that a P-SOM adaptive demodulator has a superior capability to track phase rotations caused by the Doppler effect. A theoretical noise analysis is also reported for the conventional SOM and the P-SOM. It is found that the calculation results are approximately in good agreement with the experimental ones.

Worst‐case design in head impact crashworthiness optimization

AbstractThis paper describes the solution of a worst‐case design optimization problem of head impact in automotive design. The worst‐case design process uses an optimization algorithm that can locate saddlepoints: points in the design space where the objective function is maximized with respect to some design variables (worst case) while it is minimized with respect to other design variables simultaneously. The worst‐case design methodology is first tested using two analytic functions. Both functions contain saddlepoints, while the second one also has a random analytic noise component and an integer variable. Thereafter, the methodology is applied to the worst‐case design of a crashworthiness head impact problem. The head impact problem contains both numerical noise and an integer variable. For the first analytical case, the effect of separability of the maximization and minimization variables is investigated by rotating the design variable axes. For the second analytical case, analytical noise in the form of a modified Griewank function and an integer variable is added. For the head impact problem, cases are presented where maximization and minimization are first performed separately, and then in a combined fashion to locate the saddle point. The case studies illustrate the power of this approach in the automotive occupant safety design field. Copyright © 2003 John Wiley & Sons, Ltd.

An Adaptive, Rate-Optimal Test of Linearity for Median Regression Models

This article is concerned with testing the hypothesis that a conditional median function is linear against a nonparametric alternative with unknown smoothness. We develop a test that is uniformly consistent against alternatives whose distance from the linear model converges to zero at the fastest possible rate. The test does not require knowledge of the distribution of the model's random noise component, and it permits conditional heteroscedasticity of unknown form. The numerical performance and usefulness of the test are illustrated by the results of Monte Carlo experiments and an empirical example.

Upscaling aspects of multi-resolution satellite data in spatial and frequency domains

To incorporate intelligence from NOAA/AVHRR data for defining land surface boundary in GCMs, 1.1 km resolution data have to be upscaled to 50 or 100 km. The 36.25 m resolution LISS-II data was upscaled to 72.5 m and then correlation of this upscaled 72.5 m data was studied with the observed 72.5 m resolution LISS-I data. Research results reported in this paper address to the preservation of maximum information content in the upscaled data by reducing the impact of random noise component during upscaling process. For frequency domain upscaling, 72.5 m upscaled image was obtained from 36.25 m resolution IRS LISS-II data by (i) removing high frequency component in Fourier Transform of the 36.25 m resolution image and thereafter performing inverse Fourier Transform and (ii) after applying mean, median, k-average, mode and fractal operators on the image. This method gave very high correlations with LISS-I image even in heterogeneous regions and thus holds high promise in handling the heterogeneity, which occurs in 50×50 or 100×100 square km grids over land surface. This paper also addresses to upscaling of 188 m resolution NDVI derived from WiFS data to 1100 m and its correlation with 1100 m resolution NDVI derived from AVHRR.

Some results about the optimal LQG tracking problem

The optimal LQG tracking problem is studied both for available and for unavailable state and reference, assuming that the last variable is the addition of a known deterministic component and of a random noise component. In both cases the optimal solution exists, is unique, and the optimal control is a suitable affine function of the current state and reference variable (when they are available) or of the corresponding optimal estimates (when they are not available). The minimum cost function is expressed in closed form.

Pattern matching using the blur hit–miss transform

The usefulness of the hit-miss transform (HMT) and re- lated transforms for pattern matching in document image applica- tions is examined. Although the HMT is sensitive to the types of noise found in scanned images, including both boundary and ran- dom noise, a simple extension, the blur HMT, is relatively robust. The noise immunity of the blur HMT derives from its ability to treat both types of noise together, and to remove them by appropriate dilations. In analogy with the Hausdorff metric for the distance be- tween two sets, metric generalizations for special cases of the blur HMT are derived. Whereas Hausdorff uses both directions of the directed distances between two sets, a metric derived from a special case of the blur HMT uses just one direction of the directed dis- tances between foreground and background components of two sets. For both foreground and background, the template is always the first of the directed sets. A less-restrictive metric generalization, where the disjoint foreground and background components of the template need not be set complements, is also derived. For images with a random component of noise, the blur HMT is sensitive only to the size of the noise, whereas Hausdorff matching is sensitive to its location. It is also shown how these metric functions can be derived from the distance functions of the foreground (FG) and background (BG) of an image, using dilation by the appropriate templates. The blur HMT can be used as a fast heuristic to avoid more expensive integer-based matching techniques, and it is implemented efficiently with boolean image operations. The FG and BG images are dilated with structuring elements that depend on image noise and pattern variability, and the results are then eroded with templates derived from patterns to be matched. Subsampling the patterns on a regular grid can improve speed and maintain match quality, and examples are given that indicate how to explore the parameter space. Trun- cated matches give the same result as full erosions, are much faster, and for some applications can be performed at a restricted set of locations. © 2000 SPIE and IS&T. (S1017-9909(00)00802-3)

A Non-parametric Method for the Reconstruction of Age- and Time-Dependent Incidence from the Prevalence Data of Irreversible Diseases with Differential Mortality

A method is proposed for reconstructing the time and age dependence of incidence rates from successive age-prevalence cross sections taken from the sentinel surveys of irreversible diseases when there is an important difference in mortality between the infected and susceptible subpopulations. The prevalence information at different time–age points is used to generate a surface; the time–age variations along the life line profiles of this surface and the difference in mortality rates are used to reconstruct the time and age dependence of the incidence rate. Past attempts were based on specified parametric forms for the incidence or on the hypothesis of time-invariant forms for the age–prevalence cross sections. The proposed method makes no such assumptions and is thus capable of coping with rapidly evolving prevalence situations. In the simulations carried out, it is found to be resilient to important random noise components added to a prescribed incidence rate input. The method is also tested on a real data set of successive HIV age–prevalence cross sections from Burundi coupled to differential mortality data on HIV+ and HIV− individuals. The often-made assumption that the incidence rate can be written as the product of a calendar time component and an age component is also examined. In this case, a pooling procedure is proposed to estimate the time and the age profiles of the incidence rate using the reconstructed incidence rates at all time–age points.

Narrow-band collisional activation technique for ion trap mass spectrometers.

Narrow-bandwidth signals were applied to the end caps of an ion trap mass spectrometer to excite ions during collisional activation. Excitation waveforms were created from a single-frequency component and a random noise component using a multiplier circuit. Tandem and higher order mass spectrometry experiments (MS3) can be performed without optimization of the supplemental frequency applied to the end cap electrodes. The usefulness of this method of ion excitation is demonstrated using singly and multiply protonated peptide ions as well as sodium-cationized carbohydrates.

Fidelity analysis of sampled imaging systems

Many modeling, simulation and performance analysis studies of sampled imaging systems are inherently incomplete because they are conditioned on a discrete-input, discrete-output model that only accounts for blurring during image acquisition and additive noise. For those sampled imaging systems where the effects of digital image acquisition, digital filtering and reconstruction are significant, the modeling, simulation and performance analysis should be based on a more comprehensive continuous-input, discrete-processing, continuous-output end-to-end model. This more comprehensive model should properly account for the low-pass filtering effects of image acquisition prior to sampling, the potentially important noiselike effects of the aliasing caused by sampling, additive noise due to device electronics and quantization, the generally high-boost filtering effects of digital processing, and the low-pass filtering effects of image reconstruction. This model should not, however, be so complex as to preclude significant mathematical analysis, particularly the mean-square (fidelity) type of analysis so common in linear system theory. We demonstrate that, although the mathematics of such a model is more complex, the increase in complexity is not so great as to prevent a complete fidelity-metric analysis at both the component level and at the end-to-end system level: that is, computable mean-square-based fidelity metrics are developed by which both component-level and system-level performance can be quantified. In addition, we demonstrate that system performance can be assessed qualitatively by visualizing the output image as the sum of three component images, each of which relates to a corresponding fidelity metric. The cascaded, or filtered, component accounts for the end-to-end system filtering of image acquisition, digital processing, and image reconstruction; the random noise component accounts for additive random noise, modulated by digital processing and image reconstruction filtering; and the aliased noise component accounts for the frequency folding effect of sampling, modulated by digital processing and image reconstruction filtering.

Millisecond and binary pulsars as nature's frequency standards -- II. The effects of low-frequency timing noise on residuals and measured parameters

Pulsars are the most stable natural frequency standards. They can be applied to a number of principal problems of modern astronomy and time-keeping metrology. The full exploration of pulsar properties requires obtaining unbiased estimates of the spin and orbital parameters. These estimates depend essentially on the random noise component being revealed in the residuals of time of arrivals (TOA). In the present paper, the influence of low-frequency ("red") timing noise with spectral indices from 1 to 6 on TOA residuals, variances, and covariances of estimates of measured parameters of single and binary pulsars are studied. In order to determine their functional dependence on time, an analytic technique of processing of observational data in time domain is developed which takes into account both stationary and non-stationary components of noise. Our analysis includes a simplified timing model of a binary pulsar in a circular orbit and procedure of estimation of pulsar parameters and residuals under the influence of red noise. We reconfirm that uncorrelated white noise of errors of measurements of TOA brings on gradually decreasing residuals, variances and covariances of all parameters. On the other hand, we show that any red noise causes the residuals, variances, and covariances of certain parameters to increase with time. Hence, the low frequency noise corrupts our observations and reduces experimental possibilities for better tests of General Relativity Theory. We also treat in detail the influence of a polynomial drift of noise on the residuals and fitting parameters. Results of the analitic analysis are used for discussion of a statistic describing stabilities of kinematic and dynamic pulsar time scales.

Linear and non-linear analysis using the Oldham–Zoski steady-state equation for determining heterogeneous electrode kinetics at microdisk electrodes and digital simulation of the microdisk geometry with the fast quasi-explicit finite difference method

Abstract A procedure which utilizes a linearized version of the Oldham–Zoski current-potential equation has been developed for the evaluation of electrode kinetic parameters from near-steady state voltammograms obtained at microdisk electrodes. The inherent advantage of the method is its mathematical simplicity relative to the other procedures already available in the literature. The procedure is applied to synthetic data obtained under near-steady state conditions from the fast quasi-explicit finite difference simulation of quasi-reversible electron transfer at a microdisk electrode. A procedure using non-linear optimization based on the Marquardt algorithm is also applied to the simulated data. Near-steady state voltammograms showing the effect of a potential dependent charge transfer coefficient are presented and analyzed. The robustness of the analysis is tested with voltammograms containing a random noise component and the near-steady state terms inherently present in experimental data. Application of the Oldham–Zoski equation to the simulated voltammograms enables the fidelity of both methods to be established over a wide range of heterogeneous kinetic conditions.

Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for “absolute” position coordinates, i.e., relative to a global reference frame, are 3–4 mm (north), 5–6 mm (east), and 10–12 mm (vertical) using 24 hour solutions. Corresponding velocity uncertainties for a 12 month period are about 2 mm/yr in the horizontal components and 3–4 mm/yr in the vertical component. High precision can also be achieved for relative position coordinates on short (<10 km) baselines using broadcast ephemerides and observing times as short as 3 hours, even when data are processed rapidly on site. Comparison of baseline length changes across the resurgent dome between the two GPS sites and corresponding two‐color electronic distance measurements indicates similar extension rates within error (∼2 mm/yr) once we account for a random walk noise component in both systems that may reflect spurious monument motion. Both data sets suggest a pause in deformation for a 3.5 month period in mid‐1995, when the extension rate across the dome decreased essentially to zero. Three dimensional positioning data from the two GPS stations suggest a depth (5.8±1.6 km) and location (west side of the resurgent dome) of a major inflation center, in agreement with other geodetic techniques, near the top of a magma chamber inferred from seismic data. GPS systems similar to those installed at Long Valley can provide a practical method for near real‐time monitoring and hazard assessment on many active volcanoes.

The impact of liberalization on the productive efficiency of Indian commercial banks

We examine the productive efficiency of 70 Indian commercial banks during the early stages (1986–1991) of the ongoing period of liberalization. We use data envelopment analysis to calculate radial technical efficiency scores. We then use stochastic frontier analysis to attribute variation in the calculated efficiency scores to three sources: a temporal component, an ownership component, and a random noise component. We find publicly-owned Indian banks to have been the most efficient, followed by foreign-owned banks and privately-owned Indian banks. We also find a temporal improvement in the performance of foreign-owned banks, virtually no trend in the performance of privately-owned Indian banks, and a temporal decline in the performance of publicly-owned Indian banks. We attempt to explain these patterns in terms of the government's evolving regulatory policies.

Seismic multiplets analysis and its implication in seismotectonics

Doublets analysis techniques suitable to obtain very accurate determination of arrival times of seismic phases on different stations are presented. These methodologies represent a very powerful tool to recognize the seismotectonic structures and to study the propagation characteristics of seismic waves. The signals similarity analysis, performed in the frequency and time domain, has been applied to increase the precision in arrival times definition of seismic phases generated by the same sources and having the same path. Tests on synthetic events have shown how it is possible to recognize the time delay between digital traces with a sensitivity less than the sample rate. In particular, in the time-domain analysis the results obtained using different interpolation functions (parabolic and sinc for the cross-correlation operator) are compared. The analysis slightly suffers from a random noise component added to the signal, allowing the phase picking of highly noised traces. On the contrary, the frequency domain analysis offers the best results in case of high signal-to-noise ratio, while it appears less ‘robust’ with respect to high noise influence. The application of relative location techniques on the obtained arrival times allows to define with very high detail the geometrical shape of seismogenetic structures. As an example, a case of spatial doublets, recorded by the seismic network of Northwestern Italy, that occurred during two days in an area of the Maritime Alps (Italy), has been considered. In spite of the low magnitude of the events, an accurate reconstruction of the spatial distribution of the sources was obtained, allowing to discriminate the fault plane from the auxiliary one in the focal mechanism solution.

Spaced antenna and interferometric velocity measurements with MF and VHF radars

The spaced antenna and interferometry techniques are applied to data collected on two MF radars (at Christchurch, New Zealand, and at Scott Base, in the Antarctic) and one VHF radar (the MU radar at Shigaraki, Japan). Velocity results obtained by the two techniques are compared as functions of characteristics such as the temporal scale and anisotropy of the scatter. In general, there was good agreement between the two techniques; however, when the temporal scale is small (indicating turbulent scatter) there was less agreement. The interferometry technique did not appear to be influenced greatly by anisotropy in the scatter. The interferometry technique was found to be affected by averaging of the Doppler spectra and by the use of an extra receiver. It is suggested that less averaging of the spectra results in increased random noise components in the spectra, which in the phase spectra are interpreted as scattering from a greater range of zenith angles. It was found that the use of three receivers rather than four also lead to scattering that appeared to originate from a greater range of zenith angles. These effects lead to lower interferometric velocity estimates that are more biased towards full correlation analysis (FCA) true velocities.

Response of dairy cattle to transient voltages and magnetic fields

Stray voltages in dairy facilities have been studied since the 1970s. Previous research using steady state AC and DC voltages has defined cow-contact voltage levels which may cause behavioral and associated production problems. This research was designed to address concerns over possible effects of transient voltages and magnetic fields on dairy cows. Dairy cow response to transient voltages and magnetic fields was measured. The wave forms of the transient voltages applied were: 5 cycles of 60 Hz AC with a total pulse time of 83 ms, 1 cycle of 60 Hz AC with a total pulse time of 16 ms, and 1 cycle of an AC square wave (spiking positive and negative) of 2 ms duration. Alternating magnetic fields were produced by passing 60 Hz AC fundamental frequency with 2nd and 3rd harmonic and random noise components in metal structures around the cows. The maximum magnetic field associated with this current flow was in excess of 4 gauss. A wide range of sensitivity to transient voltages was observed among cows. Response levels from 24 cows to each transient exposure were normally distributed. No responses to magnetic fields were observed. >

Modeling, analysis, and optimum design of quantized M-band filter banks

This paper provides a rigorous modeling and analysis of quantization effects in M-band subband codecs, followed by optimal filter bank design and compensation. The codec is represented by a polyphase decomposition of the analysis/synthesis filter banks and an embedded nonlinear gain-plus-additive noise model for the pdf-optimized scalar quantizers. We construct an equivalent time-invariant but nonlinear structure operating at the slow clock rate that allows us to compute the exact expression for the mean square quantization error in the reconstructed output. This error is shown to consist of two components: a distortion component and a dominant random noise component uncorrelated with the input signal. We determine the optimal paraunitary and biorthogonal FIR filter coefficients, compensators, and integer bit allocation to minimize this MSE subject to the constraints of filter length, average bit rate, and perfect reconstruction (PR) in the absence of quantizers. The biorthogonal filter bank results in a smaller MSE but the filter coefficients are very sensitive to signal statistics and to average bit constraints. By comparison, the paraunitary structure is much more robust. We also show that the null-compensated design that eliminates the distortion component is more robust than the optimally-compensated case that minimizes the total MSE, but only at nominal conditions. Both modeling and optimal design are validated by simulation in the two-channel case.

Characterization of noise during glottal vibration: Measurements performed on a mechanical model

Speech synthesis and coding schemes commonly incorporate a random noise component during voicing. It is hard to isolate this noise in recorded speech because of the inaccuracy of characterizing a modulated random process from a few nonidentical periods with a strong periodic component. Direct measurement on humans poses many clinical difficulties. Computational hydrodynamic modeling is difficult, and reliable modeling of turbulence is an unsolved problem. Here, direct steady-state measurements are made on a detailed, life-size mechanical model. A molded rubber model of the vocal cords is driven synchronously with the sampling clock so that precise repetitions of pitch periods are generated. The random component of the recording is isolated by subtracting away the periodic component (obtained by ensemble averaging across 1000 pitch periods). The noise power and its spectrum at each point in the pitch period are estimated by ensemble averaging the autocorrelations of the noise. The noise results are well explained in terms of the directly measured transglottal pressure and glottal area. In high-passed human speech, bursts of noise appear to overlap the closed-glottis interval. To explain this, it is necessary to include transit time for glottal air bursts to reach an obstruction 2–3 cm downstream. a)Also a student at MIT.

Improvements in absolute gravity observations

In the absolute gravity instruments developed by the Joint Institute for Laboratory Astrophysics (JILA) (Zumberge et al., 1982; Niebauer et al., 1986), the release of the dropped object induces systematic vibrations in the floor‐gravimeter system. These vibrations can cause significant errors in the observed time‐distance values from which the gravitational acceleration is computed. Detailed study of the vibrations affecting the gravity observations shows them to contain random noise and site dependent systematic components, which can be modeled by decaying sinusoids in the range of 10 to 120 Hz. This paper discusses (1) a mathematical filtering method to correct the observed time‐distance array by identifying and removing all non‐random signals from each individual drop, (2) upgrades of the gravimeter controller, which allow the collection of the data required to implement the mathematical filtering, and (3) mechanical filtering experiments using shock dampening pads and braces to minimize the vibrations. The maximum correction to observed gravity has been 23 μGal using the mathematical filter; typical corrections are in the 2–7 μGal range. The use of the shock dampening devices alone resulted in a three‐fold reduction in the amplitudes and decay times of the systematic vibrations.

The effects of recording medium upon reversal records

The effects of magnetic recording by different rock types upon the appearance of paleomagnetic records of reversals have been simulated using a model of transition fields. Lava records were simulated using a Poisson process. The results are characterized by hangups and impulses which are not present in the reversal model, but resemble observed lava records of reversals. Sedimentary records simulated by smoothing produce predictable attenuation of features of the model, and, if a component of random noise is added, seem to match the appearance of many observed sedimentary records. These numerical experiments suggest that many features that might be interpreted as field behavior may generated by the recording process.